The invention concerns an infinitely variable hydromechanical torque-routing transmission with multiple operating ranges selectable via switching elements. Such a transmission includes a first, mechanical part including a planetary differential gear featuring at least two sun wheels of different diameters, a ring gear and an annulus shaft on which there are arranged twin planet wheels (rotationally fixed planet wheels) which are in mesh with the sun wheels. The large sun wheel is coupled to the transmission input shaft, the annulus shaft to the transmission output shaft. Such a transmission also includes a second, hydrostatic part including two energetically coupled adjustable hydrounits which can be operated in both directions as a pump or a motor and are coupled to the mechanical part. The ring gear is coupled, in the various operating ranges, for control of the direction of rotation and speed of rotation of the transmission output shaft, to a first hydrounit. The second hydrounit is in the first operating range in drive connection with the transmission output shaft via an alternating switching element, while the first hydrounit, connected to the ring gear, operates as a pump and the second hydrounit as a motor. In the first and second operating range, the two hydrounits pass through their adjustment ranges between minimum and maximum in opposite directions, trading their functions as they switch from the first to the second operating range and vice versa.
The infinitely variable hydromechanical torque-routing transmission--hereafter briefly referred to as a SHL gearbox--is known from DE 29 04 572 and features in its hydrostatic part hydrounits capable of one-sided tilt. Performing system-specific rotational speed reversals of individual hydrounits in the various operating ranges, in braking and in reverse gear, requires in the various operating ranges a switching of flow direction in the hydrounits, which is accomplished by means of an expensive control block. The disadvantage of using a control block of this type primarily consists of the problem-prone ducting, the low structural fatigue strength and the limited options in equipping it with hydraulic control organs, as well as very high cost. Furthermore, the external dimensions of this control block are determined by the maximum volume flow of the hydrounits, the associated dimensions of installation valves, the ducting and allowable material stress, precluding an integration in a compact transmission. Moreover, the weight of the transmission is considerably increased by the control block.
The problem underlying the invention consists of advancing an SHL gearbox of the initially mentioned type in such a way that the cited disadvantages will be avoided, while at the same time attempting to obtain a minimization of the control and regulating expense.